A machine (e.g., a machining center or a laser processing machine) such as a processing machine drives a servomotor to thereby control the position of a machining head or the like. When the position of the machining head or the like is controlled, the machining head is controlled such that a route between a start point and an end point of movement accurately follows a commanded route. An axis driven by the servomotor is called feed axis. A two-dimensional or three-dimensional moving trajectory is realized by using a plurality of the feed axis.
The machining head is provided with position detectors such as encoders or linear scales at the respective feed axes. Control using feedback (hereafter, feedback control) is performed such that a difference between a position detected by the position detectors (a feedback position) and a command position decreases. Consequently, the machining head moves while following a given command route.
A trajectory of the feedback position (a feedback trajectory) desirably coincides with a trajectory of the command position (a command trajectory). However, a trajectory error actually occurs between the feedback trajectory and the command trajectory because of various factors.
In machines in recent years, machining accuracy in machining is deteriorated when the trajectory error is large. Therefore, a trajectory error at the time when a circular motion or the like is performed is measured; and adjustment of control parameters, review of a machine configuration, and the like are performed on the basis of a result of the measurement. Conventionally, when a trajectory error during a motion is evaluated, the motion is performed by using a plurality of axes. A feedback trajectory at that time is measured. For example, a numerical control device of Patent Literature 1 collects the position of a servo axis and the position of a spindle axis at the same time at every predetermined cycle, and it converts collection position data in order to calculate machining shape data.